Comments on: How I Know I Don’t Know Enough About Lisp Macros

By: olof

olof — Mon, 13 Jul 2009 15:14:28 +0000

well, you could use some reader macros to use a modified do-jump-table-cases

(defmacro do-jump-table-cases (&rest options)
  `(list ,@(loop for ii from 0
	      for oo in options
	      collecting `'(,ii ,oo)))))

like this:

(defun bar (op-code)
  #.`(ecase op-code
     ,@(do-jump-table-cases
	 (write "NOOP")
	 (write "SYNC")
 	 (write "QUIT"))))

which generates (at read time)

(defun bar (op-code)
  (ecase op-code
    (0 (write "NOOP"))
    (1 (write "SYNC"))
    (2 (write "QUIT"))))

doesn’t look so nice though

By: Lisp Jump Tables :: nklein software

Lisp Jump Tables :: nklein software — Mon, 13 Jul 2009 03:20:41 +0000

[...] few weeks back, I posted about how I know that I have more to grok about Lisp macros. In that post, I needed to explain Lisp macros a bit for those not in the know. The example that I [...]

By: Mark H.

Mark H. — Thu, 25 Jun 2009 11:51:57 +0000

It’s a concatenative macro processor, arguments are taken from an explicit stack. Here’s an example:

Example 2: 99 bottles of beer (http://99-bottles-of-beer.net/)

`drink! ( u — ) `{continue}${#}
this-many-bottles of beer on the wall, this-many-bottles of beer.
Take one down and pass it around, fewer-bottles of beer on the wall.

{repeat}`

`oh-no! ( — ) `No more bottles of beer on the wall, no more bottles of beer.`

`please! ( u — u ) `{#}
Go to the store and buy some more, this-many-bottles of beer on the wall.`

`this-many-bottles ( u — u ) `[{dup} 0& ~no more bottles~1& ~1 bottle~{.} ~ bottles~]`

`fewer-bottles ( u — u-1 ) `{–}$this-many-bottles`

99& drink!
oh-no!
99& please!

By: pat

pat — Wed, 24 Jun 2009 21:33:07 +0000

That doesn’t help me in my situation. In my situation, the enclosing macro tries to make some determination based on the number of forms it contains. If one of those forms is a (progn …), it will look like only one form instead of however many it contains.

In other situations, I want to splice something into the middle of a list… not into the middle of code.

By: mathrick

mathrick — Wed, 24 Jun 2009 19:55:58 +0000

If you want more than one form, just wrap them all in PROGN. It’s defined to preserve toplevelness, if that’s your concern, so the following will work as you’d expect it to when placed at the toplevel:

(progn
  (defclass ...)
  (defun ...)
  (defvar ...))

By: pat

pat — Sat, 20 Jun 2009 01:47:49 +0000

That’s interesting. I may have to tinker with it next time I’m thinking of using m4 for something. I’ll have to look more closely, too. I didn’t see any examples of macros with arguments.

By: Mark H.

Mark H. — Sat, 20 Jun 2009 00:57:19 +0000

While your experimenting with macros you might be interested in checking out the concatenative macro processor I’ve been working on, it’s an unusual take the topic:

http://freshmeat.net/projects/minimac-macro-processor

Cheers,
Mark H.